how to create letter "s" through nodes?
Create a half circle by attaching a colorramp to a spherical gradient and removing the bottom half greater than math.



Make these nodes into a group. CtrlG

Create a square by clamping X and Y coordinates to [-1, 1]



Rotate the items with vector math operations or mapping nodes.
Squash the square into a rectangle and place it in the center. Use the half circles for top and bottom.



We can improve this setup by using a Radial Gradient and plug it into a colorramp to control the half circle, then we can increase the angle.